The present invention relates to a drill bit, in particular for the drilling of rock. The invention has particular relevance to drill rods and to bolts of the type known as rock or roof bolts (hereinafter called “roof bolts”) and to such bolts of the self drilling kind.
Roof bolts are commonly employed in the underground mining industry to support the walls and/or the roof of excavated tunnels and openings against fragmentation and collapse. Roof bolts typically are applied by first drilling a pilot hole in the rock wall and thereafter inserting the roof bolt therein. The bolt is fixed within the hole normally by a settable glue, such as a resin or a mortar cement. Otherwise, the roof bolt can be arranged to interlock with the internal wall of the pilot opening, such as by a thread or an expanding sleeve and typically a combination of settable glue and an interlocking arrangement is employed.
Self drilling roof bolts have a drilling capacity that a simple roof bolt does not have. If a self drilling roof bolt is employed, the bolt itself can be driven to drill into the rock wall and when the bolt has sufficiently penetrated the wall, suitable fixing means, such as a settable resin may be employed. A self drilling roof bolt therefore increases the speed at which roof bolts can be installed, because it eliminates the need to remove the drill from the pilot hole to insert the roof bolt. Effectively the drilling operation and the insertion are completed at the same time. This advantageously means that the drill operator is next to the unsupported wall, or is under the unsupported roof, for a significantly reduced amount of time, thereby reducing the risk of injury to such operators.
U.S. Pat. No. 6,309,159 discloses a self drilling roof bolt which has an elongate bolt body and a drill tip attached to the leading end thereof. The drill tip extends across the end of the bolt and is supported against a pair of radially spaced, axially extending abutment elements, which engage the drill tip on opposite sides thereof. In practice the tip is secured to the abutment elements by welding, soldering or brazing.
In the self drilling roof bolt of U.S. Pat. No. 6,309,159 the type of mechanism used to secure the tip to the abutment elements adds significant cost to the roof bolt.
As the welding, soldering or brazing operation must be carefully performed so as to ensure the integrity of the connection under the highly aggressive conditions of drilling.
A further disadvantage resides in the most common form of connection which is brazing, because brazing requires expensive induction equipment for production line manufacture. Also, a brazed connection often suffers from concentricity problems between the tip and the bolt body or shank, because during brazing, it is difficult to maintain proper concentric alignment.
It is an object of the invention to provide a drill bit for a drill rod and/or a self drilling roof bolt which provides an alternative connection arrangement between the drill tip and the leading end of the rod or bolt to improve the connection therebetween and/or to facilitate connection by different means to those discussed above.